1. Field of the Invention
The present invention relates to a die for extrusion-molding that is used upon manufacturing of a porous ceramic member, and a method for manufacturing a porous ceramic member using this die for extrusion-molding.
2. Discussion of the Background
Recently, particulate matters (hereinafter, referred to as PM) contained in exhaust gases that are discharged from internal combustion engines for vehicles such as a bus, a truck and the like, construction equipment and the like, have raised serious problems as contaminants harmful to the environment and the human body.
There have been proposed various types of ceramic filters for purifying exhaust gases in which such exhaust gases pass through a porous ceramic so that the PM in exhaust gases are captured.
The ceramic filter is normally configured such that a plurality of porous ceramic members 40 as shown in FIGS. 1A, 1B and 2 are combined with one another to form a ceramic filter 50. Further, as shown in FIGS. 1A and 1B, the porous ceramic member 40 has a large number of cells 41 placed in parallel with one another in the longitudinal direction so that partition walls 43 that separate the cells 41 are allowed to function as filters.
In other words, each of the cells 41 formed in the porous ceramic member 40 has either one of the end portions on the inlet side or the outlet side of exhaust gases sealed with a plug material layer 42 as shown in FIG. 1B so that exhaust gases that have flowed into one of the cells 41 are allowed to flow out of another cell 41 after surely having passed through the partition wall 43 that separates the cells 41. When exhaust gases pass through this partition wall 43, PM is captured at the partition wall 43 portion, and thereby the exhaust gases are purified.
Note that FIG. 1A is a perspective view that schematically shows one example of a porous ceramic member; and FIG. 1B is a cross-sectional view taken along line B-B of the porous ceramic member shown in FIG. 1A. Further, FIG. 2 is a perspective view that schematically shows one example of a ceramic filter.
Conventionally, upon manufacturing such a porous ceramic member 40, a ceramic molded body 5 shown in FIGS. 3A and 3B in which a large number of cells 6 are placed in parallel with one another in the longitudinal direction with a partition wall 7 therebetween has been produced at first by mixing a ceramic powder, a binder, a dispersant solution and the like to prepare a mixed composition for producing a molded body, and then charging the mixed composition into an extrusion-molding apparatus provided with a die for extrusion-molding and carrying out an extrusion-molding process and the like. FIG. 3A is a perspective view that schematically shows the ceramic molded body 5; and FIG. 3B is a cross-sectional view taken along line A-A of the ceramic molded body shown in FIG. 3A.
After the above-mentioned process, the obtained ceramic molded body 5 is dried by using a heater and the like, and thereafter a degreasing process for thermally decomposing organic matters such as a binder and the like in the ceramic molded body 5 and a firing process for firing the ceramic are carried out. The porous ceramic member 40 has thus been manufactured.
FIG. 4A is a cross-sectional view that schematically shows a conventional die for extrusion-molding; and FIG. 4B is a perspective view that schematically shows the manner in which a ceramic molded body is produced, using an extrusion-molding apparatus provided with the die for extrusion-molding.
FIG. 5A is an enlarged front view of a die main body that constitutes an embodiment of a die for extrusion-molding; and FIG. 5B is a rear view of the die main body.
As shown in FIG. 4B, an extrusion-molding apparatus 80 is provided with a die for extrusion-molding 60 at the front end of a casing 81, and a molded body 90 is formed by being continuously pushed out through the mold for extrusion-molding 60. A screw (not shown) is provided inside the casing 81, and by this screw the material composition is mixed up and the material composition is pushed into the mold for extrusion-molding 60 so that the molded body 90 in which a large number of cells are longitudinally placed in parallel with one another is continuously manufactured. Then, the molded body 90 which has been stretched out continuously is cut into a predetermined length so that the ceramic molded body 5 is formed.
As shown in FIG. 4A, the die for extrusion-molding 60 is provided with a die main body 68 comprising a material supplying part 65 and a molding groove part 61 that are formed integrally, and an outer frame 70 for supporting and fixing the die main body 68.
Further, as shown in FIG. 4A, in the material supplying part 65, material supplying holes 66 having a truncated cone shape are formed so that the mixed composition can pass through those holes. On the other hand, in the molding groove part 61, molding grooves 62 formed in a checkered pattern as shown in FIGS. 5A and 5B are formed so that the mixed composition which has passed through the material supplying holes 66 can be molded into the shape of the ceramic molded body 5.
That is, in this molding groove part 61, a large number of pillar-shaped parts 63 having a square pillar-shape are arranged in the direction exactly perpendicular to the paper surface of the figure, and under a state in which the pillar-shaped parts 63 are supported by the members constituting the material supplying part 65. As the mixed composition continuously passes through the molding grooves 62 that are formed through arranging those pillar-shaped parts 63, the molded body 90 is manufactured.
When the extrusion-molding process is carried out by using the extrusion-molding apparatus 80, the mixed composition is charged into the casing 81. The mixed composition is further kneaded inside the extrusion-molding apparatus 80 and pushed by a screw blade (not shown) so that the mixed composition gradually moves in the direction of the end portion, passes through the molding grooves 62 inside the die for extrusion-molding 60, and is extruded. Then, the extruded material is cut into a predetermined length so that the pillar-shaped ceramic molded body 5 in which a large number of cells 6 are longitudinally placed in parallel with one another with the partition wall 7 therebetween is manufactured.
JP-A 8-90534 discloses a die for molding honeycomb structures which basically has the above-mentioned constitution, and also has a constitution in which the material supplying holes of the respective material supplying parts extend toward the upstream end portions of the respective molding grooves, and the respective upstream end portions are provided with a reservoir having a cross-sectional area larger than the respective material supplying holes.
The contents of JP-A 8-90534 are incorporated herein by reference in their entirety.